Bucket received frames by their mac receive stamp and read one bucket back

sock.go

@@ -114,6 +114,22 @@ func newMmsghdrs(bufs [][]byte) ([]mmsghdr, []unix.Iovec) {
 	return hdrs, iovs
 }
 
+// Room for one SCM_TIMESTAMPING and its three timespecs.
+const cmsgLen = 128
+
+// Receive headers carry a control buffer each, so the mac's receive stamp comes
+// back alongside every frame.
+func newRxMmsghdrs(bufs [][]byte) ([]mmsghdr, [][]byte) {
+	hdrs, _ := newMmsghdrs(bufs)
+	oob := make([][]byte, len(bufs))
+	for i := range bufs {
+		oob[i] = make([]byte, cmsgLen)
+		hdrs[i].hdr.Control = &oob[i][0]
+		hdrs[i].hdr.Controllen = cmsgLen
+	}
+	return hdrs, oob
+}
+
 func packetDrops(fd int) uint64 {
 	st, err := unix.GetsockoptTpacketStats(fd, unix.SOL_PACKET, unix.PACKET_STATISTICS)
 	if err != nil {